|Chu, Chang Chi|
|Freeman, Thomas - NORTH DAK0TA STATE UNIV.|
Submitted to: Journal of Chinese Association of Entomologists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 1998
Publication Date: N/A
Interpretive Summary: The silverleaf whitefly is a pest of vast economic proportions both because of its broad range of host plants and its resistance to pesticides. How it feeds so successfully on his broad range of hosts has been poorly under- stood because we know so little of the basic feeding biology. For example, prior to this work, we did not understand exactly where in the leaf these whiteflies feed, how they find their way to their feeding sites and different varieties and species of hosts affected feeding success. This paper synthesizes and advances our understanding of how these whiteflies and other phloem feeders succeed in exploiting its hosts. By clarifying the feeding process, it gives a basis for plant breeders and genetic engineers to develop varieties that are more resistant to whiteflies. This should lead to economic and environmental benefits from reduced dependence on pesticides and more control by biologically based technologies.
Technical Abstract: Survival of silverleaf whitefly nymphs requires stylet penetration of the smallest veins in host plant leaves. Elaborate behaviors allow insects to reach such veins. Light and electron microscopy, and cofocal imaging reveal that feeding involves probing of minor veins elements. Surface structures, as lamina trichomes and elongated epidermal cells, serve as guides for crawler to begin its probing. Nymphs use saliva to produce a branched, sleeve-like structure (a salivary sheath) that guides the stylets to veins. Most of the sheath material is extra-cellular and is built in the extensive air space between spongy parenchyma cells. Only a part of the sheaths are found inside cells, that portion being in epideral cells. Nymphs did not penetrate into mesophyll. With sectioning techniques, it appeared that some sheaths led to non-vascular tissue. However, when non-sectioned leaves were stained and cleared so that entire sheaths could be viewed intact, it became apparent that nymphs always made contact with minor veins. Sheaths were up to 140 micrometers long and about 2 micro- meters in diameter at their widest dimensions. Sheaths had the appearance of fused beads. Some sheaths were glued to cell walls and made contiguous contact betwee the plant leaf surface where penetration originated, proceeding all the way to the veins. Some sheaths terminated blindly without reaching a vein, and were invariably sealed. The relative success of B. argentifolii on different host plants is attributable to the geometry of feeding sites in relationship to the availability of minor vein This explains why cuburbit are better hosts than lettuce.